U.S. patent application number 16/645106 was filed with the patent office on 2021-01-28 for method for operating a steam turbine.
This patent application is currently assigned to Siemens Aktiengesellschaft. The applicant listed for this patent is SIEMENS AKTIENGESELLSCHAFT. Invention is credited to Matthias KOWALSKI, Roland SIEVERT.
Application Number | 20210028730 16/645106 |
Document ID | / |
Family ID | 1000005182594 |
Filed Date | 2021-01-28 |
United States Patent
Application |
20210028730 |
Kind Code |
A1 |
KOWALSKI; Matthias ; et
al. |
January 28, 2021 |
METHOD FOR OPERATING A STEAM TURBINE
Abstract
A method for operating a steam turbine, wherein the pressure of
the cooling medium in the generator is changed not only for cooling
but also for increasing or decreasing the torque of the generator
on the steam turbine, this being utilized for the purpose of the
start-up or shut-down process.
Inventors: |
KOWALSKI; Matthias; (Mulheim
an der Ruhr, DE) ; SIEVERT; Roland; (Duisburg,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SIEMENS AKTIENGESELLSCHAFT |
Munich |
|
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
Munich
DE
|
Family ID: |
1000005182594 |
Appl. No.: |
16/645106 |
Filed: |
August 21, 2018 |
PCT Filed: |
August 21, 2018 |
PCT NO: |
PCT/EP2018/072551 |
371 Date: |
March 6, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02P 9/08 20130101; F01D
19/02 20130101; F01D 15/10 20130101; F01D 25/12 20130101; F01K
7/165 20130101; H02P 2101/20 20150115 |
International
Class: |
H02P 9/08 20060101
H02P009/08; F01K 7/16 20060101 F01K007/16; F01D 15/10 20060101
F01D015/10; F01D 19/02 20060101 F01D019/02; F01D 25/12 20060101
F01D025/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2017 |
EP |
17192398.0 |
Claims
1. A method for operating a steam turbine, wherein the steam
turbine has a rotatably mounted steam turbine rotor and a housing
which is arranged around the steam turbine rotor, wherein the rotor
is coupled in terms of torque to a generator rotor of an electrical
generator, the method comprising: cooling the generator with a
cooling medium, wherein a cooling pressure of the cooling medium in
the generator is set, exerting a torque by the generator rotor on
the steam turbine rotor, changing the torque from the generator
rotor to the steam turbine rotor by means of a change in the
cooling pressure.
2. The method as claimed in claim 1, wherein an increase in the
cooling pressure leads to an increase in the torque from the
generator rotor to the steam turbine rotor.
3. The method as claimed in claim 1, wherein a reduction in the
cooling pressure leads to a reduction in the torque from the
generator rotor to the steam turbine rotor.
4. The method as claimed in claim 1, wherein the cooling pressure
is changed during a startup process of the steam turbine.
5. The method as claimed in claim 1, wherein the cooling pressure
is changed during the shutdown process of the steam turbine.
6. The method as claimed in claim 1, wherein an automation system
for regulating the cooling pressure is designed such that an
increase in the pressure and/or in the mass flow of the steam into
the steam turbine is realized within specific limits.
7. The method as claimed in claim 6, wherein the automation system
is furthermore designed such that a change, or a reduction, in the
mass flow of the steam into the steam turbine is realized within
specific limits.
8. The method as claimed in claim 7, wherein the change in the mass
flow is realized in a manner dependent on the braking load provided
by the generator.
9. The method as claimed in claim 1, wherein the cooling medium
comprises air.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the US National Stage of International
Application No. PCT/EP2018/072551 filed 21 Aug. 2018, and claims
the benefit thereof. The International Application claims the
benefit of European Application No. EP17192398 filed 21 Sep. 2017.
All of the applications are incorporated by reference herein in
their entirety.
FIELD OF INVENTION
[0002] The invention relates to a method for operating a steam
turbine, wherein the steam turbine has a rotatably mounted steam
turbine rotor and a housing which is arranged around the steam
turbine rotor, wherein the rotor is coupled in terms of torque to a
generator rotor of an electrical generator, wherein the generator
is cooled with a cooling medium, in particular air, wherein a
cooling pressure of the cooling medium in the generator is set,
wherein the generator rotor exerts a torque on the steam turbine
rotor.
BACKGROUND OF INVENTION
[0003] Steam turbines are used for example in steam power plants or
gas and steam turbine power plants, and principally have the task
of converting thermal energy into mechanical energy so as to drive
the rotor of an electrodynamic machine, in particular an electrical
generator. Here, a hot steam with relatively high thermal energy is
conducted via inflow regions into the steam turbine, wherein the
steam thermally expands, and in the process cools, on a flow path
within the steam turbine, wherein the thermal energy is converted
into rotational energy of the steam turbine rotor. During
continuous operation, the components of the steam turbine and of
the electrical generator are in a thermal state of equalization.
However, operating states which require a shutdown of the steam
turbine and, in turn, a startup of the steam turbine are
required.
[0004] The startup and shutdown of a steam turbine are
characterized by several challenges. During the startup of a steam
turbine, this is flowed through merely by a relatively small steam
mass flow. The consequence is that the available quantity of steam
is not sufficient for sufficiently homogeneous throughflow of the
end stage, the radial pressure drop consequently promoting a
tendency to separation on a hub side. It may then occur that, due
to the rotational movement of the steam turbine rotor, due to the
reverse flow and due to the resulting friction losses of the
blades, the steam is heated. The consequence of this is that the
end stage blades are continuously heated. In this case, it may
occur that the temperatures reach impermissible values and
consequently limit the availability of the steam power plant.
[0005] A further challenge is that, in a high-pressure section of
the steam turbine, with a power supply disconnection, the expansion
generates only very little power. Otherwise, the steam power plant
would enter a so-called excessive rotational speed state, which is
manifested in an increased rotational speed of the steam turbine
rotor. In this case, very high temperatures at the outlet of the
high-pressure turbine section cannot be avoided and, with a
so-called hot start, can possibly lead to a shutdown. Through
provision of braking power in the strand which is formed by the
steam turbine rotor and the rotor of the electrical generator, a
relatively high pressure drop with a corresponding temperature
reduction can in this case be realized at the high-pressure turbine
section without the rotational speed increasing in this case beyond
the nominal frequency, with the generator in this case not
outputting any electrical power.
[0006] The proposed additional braking power helps during shutdown
since the rotational speed blocking ranges (risk of resonance of
components, such as for example blades) are quickly passed through,
in particular with low-tuned end stages.
[0007] A further challenge is that the steam turbine, in particular
before and in the first expansion section, is heated through more
quickly due to an increased pressure or the associated condensation
temperature, which increases the availability of the plant.
[0008] In documents WO2009/038562 A2, WO2011/018404 A1 and US
2016/344258, various methods for operating a steam turbine are
disclosed.
[0009] It would be desirable to eliminate the aforementioned
problems.
SUMMARY OF INVENTION
[0010] It is therefore the object of the invention to specify a
method for operating a steam turbine in which the startup and
shutdown processes are improved.
[0011] Said object is achieved by a method for operating a steam
turbine, wherein the steam turbine has a rotatably mounted steam
turbine rotor and a housing which is arranged around the steam
turbine rotor, wherein the rotor is coupled in terms of torque to a
generator rotor of an electrical generator, wherein the generator
is cooled with a cooling medium, in particular air, wherein a
cooling pressure of the cooling medium in the generator is set,
wherein the generator rotor exerts a torque on the steam turbine
rotor, wherein the torque from the generator rotor to the steam
turbine rotor is changed by means of a change in the cooling medium
pressure. The object is also achieved by an automation unit for
implementing such a method.
[0012] The invention proposes the use as a brake of the generator
coupled in terms of torque to a steam turbine. Here, the generator
is cooled with air during operation. An increase in the air
pressure in the generator leads to increased gas friction losses by
way of surface friction, fan power and conveying action of the
rotor or radial fan. The torque to the steam turbine rotor that is
transmitted from the electrical generator rotor can thus be changed
by setting the pressure of the cooling air. This relationship is
utilized in order to optimally utilize the method for operating a
steam turbine, in particular during startup and shutdown.
[0013] One advantage of the invention is that, due to this
additional possibility of conversion in the form of heat in the
generator, instead of into turbine rotational speed, it is possible
for a larger steam mass flow to be conducted through the steam
turbine, or it is possible for a higher steam pressure to be set,
without introducing an excessive rotational speed.
[0014] For example, the braking power of a generator, owing to the
gas friction, can increase from approximately 1 megawatt to 2
megawatts if the air pressure of the cooling air is increased from
one bar to 2 bar. Consequently, the braking power would increase
from for example 1.5 megawatts to 2.5 megawatts. Such an increase
in the braking power could lead to a possible increase in mass flow
of approximately 66%, with respect to the comparable startup
process.
[0015] With the invention, it has been identified that the
generated additional friction losses in the generator lead to an
increase in enthalpy of the cooling gas in the generator. In this
case, the temperature is not increased; the heat capacity
correspondingly increases with increasing air density. The heat
energy is cooled in gas coolers of the generator, wherein there is
consequently a closed gas cooling circuit in the generator, or is
discharged to the surroundings in an open cooling circuit.
[0016] One advantage of the invention is that existing plants
merely have to be retrofitted or adapted in order to achieve the
effects according to the invention.
[0017] With the invention, regulation which additionally sets the
generator gas pressure with respect to the steam turbine at startup
and/or shutdown of the steam turbine is thus proposed. The plant
availability can be increased in this way. Furthermore, a reduction
in the ventilation at the steam turbine end stages is
advantageously achieved, which leads to a minimization of service
life consumption.
[0018] Furthermore, the high-pressure exhaust steam temperature of
the steam turbine is advantageously actively influenced, which
leads to an increase in availability. This, for example, allows the
so-called cold reheater line to be of a less expensive design.
Furthermore, when use is made of the method according to the
invention, startup lines could be dispensed with.
[0019] One significant advantage of the invention is the
minimization of blade fatigue with passing-through of the
rotational speed blocking ranges. This leads to significant
lengthening of the service life of the steam turbine blades.
[0020] It is also advantageous that, due to the increase in
condensation temperature during warmup, a relatively fast startup
of the steam turbine is possible.
[0021] The aforementioned properties, features and advantages of
the present invention, and the manner in which these are achieved,
will be explained in a clearer and more clearly understandable
manner in conjunction with the following description of an
exemplary embodiment.
DETAILED DESCRIPTION OF INVENTION
[0022] A steam power plant or a gas and steam turbine plant
generally has a steam turbine comprising a high-pressure turbine
section, a medium-pressure turbine section and a low-pressure
turbine section. Steam is generated in a steam generator and is
conducted via a fresh steam line to the high-pressure turbine
section. The steam flowing out of the high-pressure turbine section
is correspondingly cooled and has a relatively low pressure. This
cooled steam is conducted via a cold reheater line to a reheater
and, there, heated to a relatively high temperature again.
Subsequently, the reheated steam passes via the hot reheater line
to the medium-pressure turbine section, and then flows from the
medium-pressure turbine section to the low-pressure turbine section
and, from there, directly into a condenser, where the steam is
condensed to form water and is correspondingly conducted via pumps
to the steam generator again. The circuit is thus closed. During
the startup process, the components must be correspondingly heated,
which requires a certain period of time. The steam turbine has a
steam turbine rotor which is rotatably mounted, wherein a housing
is arranged around the steam turbine rotor. The steam turbine rotor
is coupled in terms of torque to a generator rotor. This means that
the torque of the steam turbine rotor that is generated by the
steam turbine exerts a torque on the generator rotor.
[0023] The electrical generator has a rotatably mounted generator
rotor on which a rotor winding is arranged. A relatively high
electric current flows through the rotor winding, by way of which
current a magnetic field is generated, which, by way of the
rotation, transfers an alternating magnetic field to a stator
winding of a winding of a stationary part that is situated in the
generator housing. An electric voltage is induced in the winding of
the stationary part. Due to the relatively high currents in the
rotor winding and in the stator winding, it is necessary for these
to be cooled. A winding is cooled for example with air. In this
case, the air pressure has an influence on the cooling power and on
the torque of the generator rotor, since an increase in the air
pressure results in the gas friction being increased, which leads
to gas friction losses and consequently to increased negative
torques. The stator winding may be cooled for example likewise with
air or with nitrogen or with water. The cooling pressure of the
cooling medium, cooling air in this case, can be set. An automation
unit allows the cooling pressure to be set such that the torque
from the generator rotor to the steam turbine rotor is changed,
this being utilized in particular during the startup and/or
shutdown processes. For example, during the startup process, an
increase in pressure can lead to an increased negative torque of
the generator rotor on the steam turbine rotor, which can be used
for increasing the pressures or mass flows in the steam turbine
without an excessive rotational speed.
[0024] The increase in the pressure of the cooling medium, air in
electrical generators in this case, has hitherto been used only for
the cooling. With the automation unit, regulation which
additionally sets the generator gas pressure with respect to the
desired load of the steam turbine at startup and/or shutdown of the
steam turbine is now realized.
[0025] Even though the invention has been illustrated and described
in more detail by way of the preferred exemplary embodiment, the
invention is not restricted by the examples disclosed, and other
variations may be derived therefrom by a person skilled in the art
without departing from the scope of protection of the
invention.
* * * * *